The overall objective of this project is the characterization of the structural features, number and location of the active sites of IgM antibodies. The present studies seek to further define the role of the constituent polypeptide chains in the formation of the active site using Waldenstrom's IgM proteins that bind human IgG. One of the principal goals involves refolding the IgM, after extensive denaturation, into active products. A related goal involves the restructing of active units from the isolated and extensively denatured polypeptide chains of the IgM. The conditions to be utilized include complete cleavage of the interchain disulfide bonds and the use of strong unfolding agents such as high concentrations of guanidine hydrochloride. The products obtained by the refolding process will be evaluated with respect to polypeptide chain structure and conformation, especially in terms of the relationship of these to native IgM. Of particular interest will be the identity of the effective functional unit of the active products. An effort will be made to define the way in which the micron and the kappa (or lambda) polypeptide chains influence each other in expressing the information contained in their primary structures. Related studies will attempt to characterize the relative flexibility of the IgM in terms of the spatial positions that can be assumed by the Fab portions of the molecule using ultracentrifugal techniques. In addition, the possible role of the J chain in the assembly of the IgM polypeptide chains or its subunits will be investigated.